Power generating element for liquid fuel cell, method for producing the same, and liquid fuel cell using the same

ABSTRACT

A liquid fuel cell includes a positive electrode ( 8 ) for reducing oxygen, a negative electrode ( 9 ) for oxidizing fuel, a solid electrolyte ( 10 ) placed between the positive electrode ( 8 ) and the negative electrode ( 9 ), and liquid fuel ( 4 ), wherein the positive electrode ( 8 ) and the negative electrode ( 9 ) respectively include catalyst layers ( 8   b ), ( 9   b ) with a thickness of 20 μm or more, at least one of the respective catalyst layers ( 8   b ), ( 9   b ) has a pore with a pore diameter in a range of 0.3 μm to 2.0 μm, and a pore volume of the pore is 4% or more with respect to a total pore volume. Because of this configuration, a liquid fuel cell with a high output density can be provided in which the pore configuration in the catalyst layer is optimized, and catalyst performance is exhibited sufficiently.

TECHNICAL FIELD

The present invention relates to a liquid fuel cell, and in particular,to an electric power generating element for a liquid fuel cell, and amethod for producing the same.

BACKGROUND ART

Recently, along with the spread of a cordless appliance such as apersonal computer and a mobile telephone, there is a request for thefurther miniaturization and increase in capacity of a secondary batterythat is a power source for the cordless appliance. At present, alithium-ion secondary battery has been put into practical use as asecondary battery that has a high energy density and can be reduced insize and weight, and there is an increasing demand for the lithium-ionsecondary battery as a portable power source. However, the lithium-ionsecondary battery has not reached such a level as to ensure a sufficientcontinuous use time, depending upon the type of a cordless appliance tobe used.

Under such circumstances, as a battery that can satisfy theabove-mentioned demand, there are a direct methanol type fuel cell(DMFC) using liquid fuel directly for the reaction of a cell and apolymer electrolyte fuel cell (PEFC) using hydrogen for the reaction ofa cell. The DMFC has been mainly developed as a portable power source,and the PEFC has drawn attention mainly as a power source for anautomobile and a household dispersion-type power source.

In the DMFC and PEFC, electric power generating elements are composed ofsubstantially the same material. More specifically, carbon with a highspecific surface area supporting platinum (Pt) or the like, for example,is used for a catalyst of a positive electrode. A proton conductivesolid polymer film or the like, for example, is used for a solidelectrolyte. Carbon with a high specific surface area supporting aplatinum-ruthenium (PtRu) alloy or the like, for example, is used for acatalyst of a negative electrode. Although Pt is most excellent as thecatalyst of the negative electrode in the PEFC, a PtRu alloy is used inorder to suppress poisoning by carbon monoxide (CO) contained in aslight amount in hydrogen fuel. The largest difference between the DMFCand the PEFC lies in the following: the PEFC requires a reformer forproducing hydrogen that is fuel from methanol, gasoline, natural gas, orthe like, while the DMFC requires no reformer. Therefore, the DMFC canbe made compact, and recently has drawn attention as a portable powersource.

However, under the current circumferences, the output density of theDMFC is considerably lower than that of the PEFC. One of the reasons isthat the ability of the catalyst required for oxidizing methanol at thenegative electrode is not sufficient in the DMFC. The currently usedmost excellent catalyst of the negative electrode is a PtRu alloy usedeven in the PEFC. The DMFC compensates for the low catalyst ability tosome degree by using the catalyst supporting the PtRu alloy at carbon ina larger amount, compared with that of the PEFC. The specific catalystamount per electrode area of the PEFC is 0.01 mg/cm² to 0.3 mg/cm²,while that of the DMFC is 0.5 mg/cm² to 20 mg/cm².

Furthermore, the DMFC requires a large amount of catalyst similarly evenat the positive electrode. This is caused by the fact that methanolpasses through a solid polymer film to reach the positive electrode.That is, methanol that has reached the positive electrode effects aburning reaction with oxygen on the catalyst of the positive electrode,which reduces the catalyst that can be used for the oxygen-reducingreaction that is an original battery reaction at the positive electrode.Thus, even at the positive electrode, it is necessary to use a catalystin an amount larger than that required for the original oxygen-reducingreaction. Therefore, the DMFC requires a catalyst in an amount largerthan that of the PEFC even at the positive electrode. Although thetransmission of hydrogen occurs even in the PEFC, the amount thereof issmall, and the influence thereof is much smaller than that of the DMFC.

Thus, in spite of the fact that the DMFC uses a catalyst in an amountlarger than that of the PEFC, a satisfactory output density has not beenobtained. In order to achieve the further enhancement of the outputdensity of the DMFC in the future, it is necessary to consider theelectrode configuration for enhancing the utilization factor of acatalyst. More specifically, it is necessary to optimize the poreconfiguration for allowing air (oxygen) and methanol to reach eachreaction place in an electrode.

On the other hand, various kinds of techniques of optimizing the poreconfiguration in a catalyst layer of the PEFC have been proposedconventionally (see Patent Documents 1 to 6). In Patent Document 1, asolid polymer electrolyte solution in a coated catalyst layer iscoagulated in a wet state, and the pore diameter of the catalyst layeris distributed in a range of 0.05 μm to 5 μm, whereby the poreconfiguration is optimized. In Patent Document 2, particles of 0.5 μm to50 μm or sol particles of 10 nm to 100 nm are added to set the averagepore diameter of a catalyst layer to be 0.1 μm to 10 μm and the porevolume to be 0.1 cm³/g to 1.5 cm³/g, whereby the pore configuration isoptimized. In addition, as an example of a method for producing anelectrode, paying attention to the pore diameter of the catalyst layer,0.04 μm to 1.0 μm are set to be optimum values of the pore diameter inPatent Document 3, 10 μm to 30 μm are set to be optimum values of thepore diameter in Patent Document 4, 0.5 μm or less are set to be optimumvalues of the pore diameter in Patent Document 5, and 0.06 μm to 1 μmare set to be optimum values of the pore diameter in Patent Document 6.

-   -   Patent Document 1: JP 2000-353528 A    -   Patent Document 2: JP 2001-202970 A    -   Patent Document 3: JP 8(1996)-88007 A    -   Patent Document 4: JP 2002-110202 A    -   Patent Document 5: JP 2002-134120 A    -   Patent Document 6: JP 2003-151564 A

However, in the DMFC, a larger amount of catalyst is used compared withthe PEFC as described above, and the catalyst layer is thicker than thatof the PEFC. Therefore, in order to allow air (oxygen) and methanol toreach the inside of the catalyst layer, the pore of the catalyst layerof the DMFC needs to be larger than that of the catalyst layer of thePEFC. On the other hand, in the DMFC in which the catalyst layer isthick, when the pore of the catalyst layer is too large, the electronconductivity and ion conductivity decrease remarkably. Therefore, evenwhen the techniques of the above-mentioned Patent Documents 1 to 6proposed as the techniques of optimizing the pore configuration in thecatalyst layer of the PEFC are directly applied to the DMFC, asufficient output density cannot be obtained.

Thus, the pore configuration of the catalyst layer of the DMFC requiresan optimization technique of its own, different from that of the PEFC.However, such an optimization technique has not been proposed atpresent.

DISCLOSURE OF INVENTION

An electric power generating element for a liquid fuel cell of one ormore embodiments of the present invention includes: a positive electrodefor reducing oxygen; a negative electrode for oxidizing fuel; and asolid electrolyte placed between the positive electrode and the negativeelectrode, wherein the positive electrode and the negative electroderespectively include a catalyst layer with a thickness of 20 μm or more,at least one of the respective catalyst layers has a pore with a porediameter in a range of 0.3 μm to 2.0 μm, and a pore volume of the poreis 4% or more with respect to a total pore volume.

Furthermore, the liquid fuel cell of one or more embodiments of thepresent invention includes the above-mentioned electric power generatingelement for a liquid fuel cell and liquid fuel.

A method for producing an electric power generating element for a liquidfuel cell of one or more embodiments of the present invention is amethod for producing the above-mentioned electric power generatingelement for a liquid fuel cell, which includes, as a production processof the catalyst layer, dispersing a material containing a catalyst and aproton conductive material in a solvent, forming complex particles byremoving the solvent to coagulate the material, and crushing the complexparticles.

Furthermore, a method for producing an electric power generating elementfor a liquid fuel cell of one or more embodiments of the presentinvention is a method for producing the above-mentioned electric powergenerating element for a liquid fuel cell, which includes, as aproduction process of the catalyst layer, forming complex particles bygranulating a material containing a catalyst and a proton conductivematerial.

According to one or more embodiments of the present invention, byoptimizing the pore configuration in the catalyst layer, a liquid fuelcell with a high output density can be provided in which air (oxygen)and liquid fuel are allowed to reach each reaction place in theelectrodes easily without decreasing the electron conductivity and theion conductivity, and a catalyst ability is exhibited sufficiently.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1 is a cross-sectional view showing an example of a liquidfuel cell of one embodiment of the present invention.

[FIG. 2] FIG. 2 is a cross-sectional view showing an example of anelectric power generating element for a liquid fuel cell of oneembodiment of the present invention.

DESCRIPTION OF THE INVENTION

First, an embodiment of an electric power generating element for aliquid fuel cell of the present invention will be described. An exampleof the electric power generating element for a liquid fuel cell of thepresent invention includes a positive electrode for reducing oxygen, anegative electrode for oxidizing fuel, and a solid electrolyte placedbetween the positive electrode and the negative electrode. The positiveelectrode and the negative electrode respectively include a catalystlayer with a thickness of 20 μm or more, preferably 40 μm or more. Atleast one of the respective catalyst layers has a pore with a porediameter of 0.3 μm to 2.0 μm, and the pore volume is 4% or more,preferably 8% or more with respect to the total pore volume.

In the present invention, it is assumed that the total pore volume isdetermined with respect to a pore having a pore diameter in a range of10 nm to 100 μm.

When the capacity of a pore with a pore diameter of 0.3 μm to 2.0 μm inthe catalyst layer is 4% or more with respect to the total pore volume,an electric power generating element for a liquid fuel cell with a highoutput density can be provided in which air (oxygen) and liquid fuel arelikely to reach the respective reaction places in the positive electrodeand the negative electrode, respectively, without decreasing theelectron conductivity and the ion conductivity, and each catalystability is exhibited sufficiently.

The upper limit value of the proportion of the pore volume preferably is40% or less. This is because when the proportion of the pore volumeexceeds 40%, it becomes difficult to produce the catalyst layer.

The reason why the thickness of the catalyst layer is set to be 20 μm ormore is that the catalyst layer is allowed to hold a large amount ofcatalyst so as to solve the above-mentioned problems specific to theDMFC. As long as the catalyst in the current state is used, when thethickness of the catalyst layer is below 20 μm, a sufficient outputdensity cannot be obtained. In the electric power generating element fora liquid fuel cell of the present embodiment, even when the catalystlayer is thick, an electric power generating element for a liquid fuelcell with a high output density can be provided.

The amount of the catalyst contained in the catalyst layer is desirably0.5 mg/cm² or more per unit area, more desirably 1.5 mg/cm² or more, andmost desirably 3 mg/cm² or more, so as to make it easy to obtain theeffect of the present invention. On the other hand, according to one ormore embodiments of the present invention, the utilization factor of thecatalyst is enhanced, so that sufficient reactivity is obtained evenwith a relatively small amount of catalyst, whereby a sufficient outputdensity is obtained even in the amount of 5 mg/cm² or less.

Furthermore, in the electric power generating element for a liquid fuelcell of the present embodiment, it is preferable that a positiveelectrode, a negative electrode, and a solid electrolyte form anelectrode-electrolyte assembly, and a plurality of electrode-electrolyteassemblies are arranged on an identical plane. This is because thethickness of the battery can be decreased.

The negative electrode is configured, for example, by laminating adiffusion layer made of a porous carbon material, a conductive materialsupporting a catalyst, and a catalyst layer composed of a protonconductive material and a fluorine resin binder.

The negative electrode has a function of oxidizing liquid fuel such asmethanol, and for example, platinum fine particles, alloy fine particlesof platinum and iron, nickel, cobalt, tin, ruthenium, gold, etc., andthe like are used. However, the present invention is not limitedthereto.

As the conductive material that is a support of the catalyst, forexample, carbon powder such as carbon black with a BET specific surfacearea of 10 m²/g to 2000 m²/g and a particle diameter of 20 nm to 100 nmis used. The above-mentioned catalyst is supported on the carbon powder,for example, using a colloidal method. The weight ratio between thecarbon powder and the catalyst is preferably 5 parts by weight to 400parts by weight of the catalyst with respect to 100 parts by weight ofcarbon powder for the following reason. In this range, sufficientcatalyst activity is obtained, and the particle diameter of the catalystdoes not become too large, so that the catalyst activity does notdecrease.

As the proton conductive material, for example, resin having a sulfogroup, such as polyperfluorosulfonic acid resin, sulfonated polyethersulfonic acid resin, or sulfonated polyimide resin can be used. However,the present invention is not limited thereto. It is preferable that thecontent of the proton conductive material is 2 to 200 parts by weightwith respect to 100 parts by weight of catalyst-supporting carbonpowder. In this range, sufficient proton conductivity is obtained, theelectric resistance does not become large, and the battery performancedoes not decrease.

Furthermore, as the fluorine resin binder, for example,polytetrafluoroethylene (PTFE),tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA),tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-ethylene copolymer (E/TFE), polyvinylidenefluoride(PVDF), or polychlorotrifluoroethylene (PCTFE) can be used. However, thepresent invention is not limited thereto. It is preferable that thecontent of the fluorine resin binder is 0.01 parts by weight to 100parts by weight with respect to 100 parts by weight ofcatalyst-supporting carbon powder for the following reason. In thisrange, a sufficient binding property is obtained, electric resistantdoes not increase, and battery performance does not decrease.

The positive electrode is configured, for example, by laminating adiffusion layer composed of a porous carbon material and a catalystlayer composed of carbon powder supporting a catalyst, a protonconductive material, and a fluorine resin binder. The positive electrodehas a function of reducing oxygen, and can be configured substantiallyin the same way as in the negative electrode.

In the liquid fuel cell, a so-called cross-over may arise, in whichliquid fuel passes through a solid electrolyte from a negative electrodeside to enter a positive electrode side, and reacts with oxygen on acatalyst of the positive electrode to degrade the potential of thepositive electrode. In such a case, by providing an oxidation catalystlayer for oxidizing liquid fuel between the solid electrolyte and thecatalyst layer of the positive electrode, the liquid fuel is oxidizedbefore reaching the catalyst layer of the positive electrode, therebysuppressing the cross-over.

In order to prevent the reaction in the oxidation catalyst layer frominfluencing the potential of the positive electrode, it is desirable toinclude an insulating material in the oxidation catalyst layer toprevent the conduction between the catalyst in the oxidation catalystlayer and the catalyst layer of the positive electrode. For example, amaterial (complex material) obtained by allowing an insulating materialto support a catalyst for oxidizing liquid fuel to be complexed can becontained in the oxidation catalyst layer.

There is no particular limit to the insulating material contained in theoxidation catalyst layer. Inorganic materials such as silica, alumina,titania, and zirconia, and resin such as PTFE, polyethylene,polypropylene, nylon, polyester, ionomer, butyl rubber, anethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer,and an ethylene-acrylic acid copolymer are used. The BET specificsurface area of the insulating material preferably is 10 m²/g to 2000m²/g, and the average particle diameter preferably is 20 nm to 100 nm.The catalyst can be supported on the insulating material, for example,by a colloidal method.

Furthermore, as the catalyst used in the oxidation catalyst layer, thesame catalyst as that used in the catalyst layer of the positiveelectrode or the negative electrode can be used.

The weight ratio between the insulating material and the catalystpreferably is 5 to 400 parts by weight of the catalyst with respect to100 parts by weight of the insulating material for the following reason.In this range, sufficient catalyst activity can be obtained.Furthermore, for example, in the case where a complex material isproduced by a process of precipitating a catalyst on an insulatingmaterial by a colloidal method or the like, as long as the weight ratiobetween the insulating material and the catalyst is in the above range,the diameter of the catalyst does not become too large, and sufficientcatalyst activity can be obtained.

On the other hand, in order to keep the proton conductivity between thesolid electrolyte and the catalyst layer of the positive electrode, itis desirable that a proton conductive material is contained in theoxidation catalyst layer. Furthermore, by setting the oxidation catalystlayer in a porous configuration, oxygen is likely to be supplied to thecatalyst in the oxidation catalyst layer, and the liquid fuel can beoxidized efficiently in the oxidation catalyst layer.

There is no particular limit to the proton conductive material containedin the oxidation catalyst layer. For example, the same proton conductivematerial as that contained in the catalyst layer of the positiveelectrode and the negative electrode can be used. It is preferable thatthe content of the proton conductive material contained in the oxidationcatalyst layer is 5 to 900 parts by weight with respect to 100 parts byweight of the complex material supporting the catalyst for the followingreason. In this range, sufficient proton conductivity is obtained,diffusion property of air is satisfactory, and liquid fuel can beoxidized sufficiently.

The oxidation catalyst layer can contain a binder, if required. There isno particular limit to the kind of the binder. However, the same binderas that used in the catalyst layer of the positive electrode or thenegative electrode can be used. Furthermore, it is preferable that thecontent of the binder in the oxidation catalyst layer is 0.01 to 100parts by weight with respect to 100 parts by weight of complex materialsupporting the catalyst for the following reason. In this range,sufficient binding property is obtained regarding the oxidation catalystlayer, and liquid fuel can be oxidized sufficiently without remarkablyimpairing the proton conductivity.

The solid electrolyte is composed of a material having no electronconductivity, capable of transporting a proton. For example, the solidelectrolyte can be composed of a polyperfluorosulfonic acid resin film,specifically, “Nafion” (Trade Name) produced by Dupont, “Flemion” (TradeName) produced by Asahi Glass Co., Ltd., “Aciplex” (Trade Name) producedby Asahikasei Ind. Co., Ltd., or the like. Alternatively, the solidelectrolyte also can be composed of a sulfonated polyether sulfonic acidresin film, a sulfonated polyimide resin film, a sulfuric acid dopedpolybenzimidazole film, or the like.

Next, an embodiment of a method for producing an electric powergenerating element for a liquid fuel cell of the present invention willbe described. An example of a method for producing an electric powergenerating element for a liquid fuel cell of the present inventionincludes, as the steps of producing a catalyst layer, dispersing amaterial containing a catalyst and a proton conductive material in asolvent, removing the solvent to allow the material to coagulate,thereby forming complex particles, and crushing the complex particles.

Furthermore, another example of the method for producing an electricpower generating element for a liquid fuel cell of the present inventionincludes, as the steps of producing a catalyst layer, mixing thecatalyst and the proton conductive material to granulate them, therebyforming complex particles.

By forming the complex particles, it becomes easy to control theparticle diameter of the material particles contained in the catalystlayer, and to set the volume of a pore with a pore diameter of 0.3 to2.0 μm in the catalyst layer to be 4% or more with respect to the totalpore volume.

As the specific method for forming complex particles, it is preferableto use a method for dispersing carbon powder supporting a precious metalcatalyst and proton conductive resin in lower saturated monovalentalcohol aqueous solution (solvent), removing the solvent to allow thedispersion to coagulate, followed by crushing, thereby forming complexparticles, and a method for mixing carbon powder supporting a preciousmetal catalyst and proton conductive resin and granulating them, therebyforming complex particles. As the granulation method, rollinggranulation, vibration granulation, mixing granulation, crackinggranulation, rolling fluidized granulation, granulation by a spray drymethod, or the like can be adopted.

As a method for setting the volume of a pore with a pore diameter of 0.3to 2.0 μm in the catalyst layer to be 4% or more with respect to thetotal pore volume (method for controlling the distribution of holes),there also is a method for adding inorganic particles and a fibrousmaterial relatively larger than carbon powder supporting a catalyst. Forexample, by adding inorganic particles such as graphite, alumina,silica, or titania, and organic fibers such as nylon, polyethylene,polyimide, or polypropylene, the distribution of holes can be limited.

Hereinafter, a method for producing an electric power generating elementfor a fuel cell using the above-mentioned material will be describedspecifically. First, carbon powder supporting the above-mentionedcatalyst, a proton conductive material, and a fluorine resin binder aredispersed uniformly in a solvent composed of water and lower saturatedmonovalent alcohol. It is preferable that a solid content is 1 to 70% byweight with respect to the total weight of a dispersion. When the solidcontent is less than 1% by weight, sufficient viscosity is not obtained,and workability is unsatisfactory. When the solid content is more than70% by weight, viscosity becomes too high, and workability becomesunsatisfactory. The dispersion can be performed using, for example, aball mill, a jet mill, or an ultrasonic disperser. However, the presentinvention is not limited thereto.

Next, a slurry obtained by dispersion is dried under reduced pressure toremove a solvent. This coagulates a solid content to form complexparticles. Thereafter, the complex particles are crushed to apredetermined particle diameter. The particle diameter preferably is 0.1μm to 3000 μm. When the particle diameter is less than 0.1 μm, a holesize after an electrode is produced becomes small, which decreases thediffusibility of air (oxygen) or liquid fuel. When the particle diameterexceeds 3000 μm, a hole size becomes too large, so that the electronconductivity and ion conductivity of an electrode decrease. A crushingmethod can be performed using, for example, a roller mill, a hammermill, a ball mill, or an angmill. However, the present invention is notlimited thereto. Next, the crushed complex particles are uniformlydispersed in a mixed solution of water and lower saturated monovalentalcohol to obtain a slurry. At this time, it is preferable that thesolid content is 1 to 70% by weight with respect to the total weight ofthe dispersion. When the solid content is less than 1% by weight,sufficient viscosity is not obtained, and workability is unsatisfactory.When the solid content is more than 70% by weight, viscosity becomes toohigh, and workability becomes unsatisfactory. The dispersion isperformed to such a degree that coagulated complex particles do notcollapse. The dispersion is performed using, for example, a ball mill, ajet mill, or an ultrasonic disperser. However, the present invention isnot limited thereto.

Thereafter, the slurry obtained as described above is applied to adiffusion layer made of a porous carbon material, followed by drying.Then, the resultant diffusion layer is heat-pressed to allow a binder tobe bound by melting, whereby an electrode is formed. The temperature ofthe heat press is varied depending upon the kind of a binder, andpreferably is set to be a temperature equal to or higher than the glasstransition temperature of a binder to be used, and equal to or lowerthan a temperature exceeding the glass transition temperature by 20° C.The pressure of the press preferably is 3 to 50 MPa. When the pressureof the press is less than 3 MPa, the molding of the electrode is notsufficient. When the pressure of the press exceeds 50 MPa, pores in theelectrode collapse, which decreases the battery performance.

Then, a solid electrolyte is sandwiched between the electrodes so thatthe catalyst layers of the electrodes come into contact with the solidelectrolyte, and compressed with a heat-press to produce anelectrode-electrolyte assembly. The temperature of the heat-presspreferably is set to be 100° C. to 180° C. The pressure of the presspreferably is 3 to 50 MPa. When the temperature of the heat-press isless than 100° C. and the pressure thereof is less than 3 MPa, theformation of the electrodes is insufficient. When the temperature of theheat-press exceeds 180° C., and the pressure thereof exceeds 50 MPa, thepores in the electrodes collapse, which decreases the batteryperformance.

In the case of providing an oxidation catalyst layer that oxidizesliquid fuel between the solid electrolyte and the catalyst layer of thepositive electrode, the oxidation catalyst layer may be formedpreviously on the catalyst layer of the positive electrode or the solidelectrolyte, and thereafter, the positive electrode may be integratedwith the solid electrolyte.

The oxidation catalyst layer is produced for example as follows. Acomplex material in which an insulating material supports a catalystsuch as platinum, a proton conductive material, and a fluorine resinbinder are dispersed uniformly in a mixed solvent containing water andlower saturated monovalent alcohol to obtain a slurry. At this time, itis preferable that the solid content is 1 to 70% by weight with respectto the total weight of the slurry. When the solid content is less than1% by weight, sufficient viscosity is not obtained, so that workabilityis unsatisfactory. When the solid content exceeds 70% by weight,viscosity becomes too high, and workability becomes unsatisfactory.

There is no particular limit to the above-mentioned method fordispersing a solid content. The solid content can be dispersed by thesame method as that for forming a catalyst layer of a positiveelectrode. More specifically, the obtained slurry is applied to thecatalyst layer side of the positive electrode, followed by drying. Then,the catalyst layer with the slurry applied thereto are heat-pressed tobind a binder in the slurry by melting, whereby an oxidation catalystlayer is obtained. The temperature and pressure of the heat-press varydepending upon the kind of the binder. They may be the same as thoseused to form the catalyst layer of a positive electrode. When thepressure is too low, the moldability of the oxidation catalyst layer isunsatisfactory. When the pressure is too high, the pores in theoxidation catalyst layer collapse, which decreases the batteryperformance.

The thickness of the oxidation catalyst layer preferably is 1 to 200 μmafter the production of the electrode-electrolyte assembly and beforethe electrode-electrolyte assembly is incorporated as a component of afuel cell. When the thickness of the oxidation catalyst layer is toosmall, the amount of a catalyst for oxidizing liquid fuel and reducingoxygen becomes insufficient. When the thickness of the oxidationcatalyst layer is too large, proton conductivity decreases and thebattery performance degrades. Even under the condition that theelectrode-electrolyte assembly is incorporated as a component of a fuelcell, it is desirable that the thickness of the oxidation catalyst layerhardly varies from what it was before the incorporation (i.e., about 1to 200 μm).

Next, an embodiment of a liquid fuel cell of the present invention willbe described with reference to the drawings. FIG. 1 is a cross-sectionalview showing an example of the liquid fuel cell of the presentinvention. In FIG. 1, for ease of understanding of the drawings, theratio of sizes of respective components is altered appropriately.

A positive electrode 8 is configured, for example, by laminating adiffusion layer 8 a made of a porous carbon material and a catalystlayer 8 b containing carbon powder supporting a catalyst.

A solid electrolyte 10 is made of a material having no electronconductivity, capable of transporting a proton.

A negative electrode 9 is composed of a diffusion layer 9 a and acatalyst layer 9 b, and has a function of generating a proton from fuel(i.e., a function of oxidizing fuel). The negative electrode 9 can beconfigured, for example, in the same way as in the above-mentionedpositive electrode.

The positive electrode 8, the negative electrode 9, and a solidelectrolyte 10 are laminated to form an electrode-electrolyte assembly.That is, the electrode-electrolyte assembly is composed of the positiveelectrode 8, the negative electrode 9, and the solid electrolyte 10provided between the positive electrode 8 and the negative electrode 9.Furthermore, the electrode-electrolyte assembly is arranged in a pluralnumber on an identical plane in an identical battery container.

On a side of the negative electrode 9 opposite to the solid electrolyte10, a fuel tank 3 for storing liquid fuel 4 is provided so as to beadjacent to the negative electrode 9. As the liquid fuel 4, for example,a methanol aqueous solution, an ethanol aqueous solution, dimethylether, a hydrogenerated boron sodium aqueous solution, a hydrogeneratedboron potassium aqueous solution, a hydrogenated boron lithium aqueoussolution, or the like is used. The fuel tank 3 is composed of, forexample, resin such as PTFE, hard polyvinyl chloride, polypropylene, orpolyethylene, or corrosion-resistant metal such as stainless steel. Whenthe fuel tank 3 is composed of metal, it is necessary to introduce aninsulator so that the respective negative electrodes arranged in theidentical battery container are not short-circuited electrically. In aportion of the fuel tank 3 in contact with the negative electrode 9, afuel supply hole 3 a is provided, and the liquid fuel 4 is supplied tothe negative electrode 9 through this portion. Furthermore, a fuelsuction member 5, which is impregnated with the liquid fuel 4 andsupplies the liquid fuel 4 to the negative electrode 9, is providedinside the fuel tank 3 including the portion in contact with thenegative electrode 9. Because of this, even if the liquid fuel 4 isconsumed, the contact between the liquid fuel 4 and the negativeelectrode 9 is kept, so that the liquid fuel 4 can be used up. Althoughglass fibers can be used as the fuel suction member 5, other materialsmay be used as long as they are chemically stable with the size thereofhardly varied due to the impregnation of the liquid fuel 4.

On a side of the positive electrode 8 opposite to the solid electrolyte10, a cover plate 2 is provided, and an air hole 1 is provided in aportion of the cover plate 2 in contact with the positive electrode 8.Because of this, oxygen in the air comes into contact with the positiveelectrode 8 through the air hole 1. At an end of the cover plate 2, agas-liquid separation hole and fuel filling port 6 b passing through thecover plate 2 and the fuel tank 3 is provided. On a side of thegas-liquid separation hole and fuel filling port 6 b opposite to thefuel tank 3, a detachable gas-liquid separation film 6 a is provided.The gas-liquid separation film 6 a is made of a PTFE sheet having apore, and is capable of releasing carbon dioxide generated in thedischarge reaction from the fuel tank 3 without allowing the liquid fuel4 to leak. Furthermore, by setting the gas-liquid separation film 6 a tobe detachable, a filling portion for supplementing the liquid fuel 4 isobtained. The gas-liquid separation hole and fuel filling portion 6 b,the cover plate 2, and the air hole 1 are made of, for example, the samematerial as that of the fuel tank 3.

The positive electrode 8 and the negative electrode 9 of theelectrode-electrolyte assembly adjacent to the positive electrode 8 areelectrically connected to each other with a collector 7. The collector 7connects the adjacent electrode-electrolyte assemblies electrically toeach other in a series, and all the electrode-electrolyte assembliesarranged in the identical battery container are connected electricallyin series with the collector 7. The collector 7 is composed of preciousmetal such as platinum and gold, corrosion-resistant metal such asstainless steel, carbon, or the like.

FIG. 1 shows the example using the electric power generating element fora liquid fuel cell in which an oxidation catalyst layer is not placedbetween the solid electrolyte 10 and the catalyst layer 8 b of thepositive electrode 8. In FIG. 1, the oxidation catalyst layer also canbe placed as shown in FIG. 2. FIG. 2 is a cross-sectional view showingan example of the electric power generating element for a liquid fuelbattery of the present invention, and shows an example in which anoxidation catalyst layer 11 for oxidizing liquid fuel is providedbetween the solid electrolyte 10 and the catalyst layer 8 b of thepositive electrode 8. In FIG. 2, the same components as those in FIG. 1are denoted with the same reference numerals as those therein, and thedescription thereof is omitted.

Hereinafter, embodiments of the present invention will be describedspecifically by way of examples. The present invention is not limited tothe following examples.

EXAMPLE 1

A liquid fuel cell with the same configuration as that in FIG. 1 wasproduced as follows.

A catalyst layer of a positive electrode was produced as follows. First,50 parts by weight of “Ketchen Black EC” (Trade Name) produced by LionAkzo Co., Ltd., 7 parts by weight of platinum-supporting carbon with anaverage particle diameter of 5 μm supporting 50% by weight of platinumfine particles with an average particle diameter of 3 nm, 86 parts byweight of a proton conductive material “Nafion” (Trade Name, theconcentration of a solid content is 5% by weight) produced byElectroChem Inc., and 7 parts by weight of water were preparedrespectively. They were mixed and dispersed uniformly with an ultrasonicdisperser, and the obtained slurry was dried under reduced pressure toremove a solvent. Complex particles coagulated by drying were crushedwith a planetary ball mill at a rotation number of 200 rpm for one hour.Consequently, complex particles with an average particle diameter of 10μm were obtained.

Next, 10 parts by weight of the obtained complex particles were added to89 parts by weight of water and one part by weight of 1-propanol, andthe resultant mixture was stirred with a stirrer at a rotation number of100 rpm for one minute, whereby a slurry with the complex particlesdispersed therein was obtained. The obtained slurry was applied to onesurface of a solid electrolyte “Nafion 117” (Trade Name, thickness: 180μm) produced by Dupont so that the amount of platinum became 3.0 mg/cm²,followed by drying, whereby a catalyst layer of a positive electrode wasformed on one surface of the solid electrolyte.

A catalyst layer of a negative electrode was produced as follows. First,50 parts by weight of the above-mentioned “Ketchen Black EC”, 7 parts byweight of platinum-supporting carbon with an average particle diameterof 3 μm supporting 50% by weight of platinum-ruthenium alloy (alloyweight ratio 1:1) fine particles with an average particle diameter of 3nm, 86 parts by weight of the above-mentioned “Nafion”, and 7 parts byweight of water were prepared respectively. They were mixed anddispersed uniformly with an ultrasonic disperser, and the obtainedslurry was dried under reduced pressure to remove a solvent. Complexparticles coagulated by drying were crushed with a planetary ball millat a rotation number of 200 rpm for one hour. Consequently, complexparticles with an average particle diameter of 9 μm were obtained. Next,a catalyst layer of a negative electrode was formed in the same way asin the positive electrode, except that the complex particles wereapplied to one surface of the solid electrolyte opposite to the surfacewhere the catalyst layer of the positive electrode has been formed sothat the amount of platinum-ruthenium became 3.0 mg/cm².

Next, the laminate of the catalyst layer of the positive electrode, thesolid electrolyte, and the catalyst layer of the negative electrodeformed as described above was heat-pressed at 120° C. for 3 minutesunder the condition of 10 MPa, whereby an electrode-electrolyte assemblywas produced. The electrode area was set to be 10 cm² in both thepositive and negative electrodes.

The cross-section of the obtained electrode-electrolyte assembly wasobserved with an electron microscope, revealing that the thickness ofthe catalyst layer of the positive electrode was 52 μm, and thethickness of the catalyst layer of the negative electrode was 50 μm. Thepore distribution of each catalyst layer of the obtainedelectrode-electrolyte assembly was measured with a mercury porosimeter“Pore Sizer 9310” (Trade Name) produced by Micromeritics. Consequently,in any of the catalyst layers, the volume of a pore with a pore diameterof 0.3 μm to 2.0 μm was 10% with respect to the total pore volume.

As the diffusion layer, a carbon cloth with a thickness of 400 μm wasused. Furthermore, a cover plate and a fuel tank provided on a side ofthe positive electrode opposite to the solid electrolyte respectivelywere composed of stainless steel (SUS316) coated with a phenol resinbased coating “Micas A” (Trade Name) produced by Nippon Paint Co., Ltd.,as an insulating coating film. A positive collector was made of a goldsheet with a thickness of 10 μm, and attached to the positive electrodewith epoxy resin. As the liquid fuel, 5% by weight of methanol aqueoussolution was used. A negative collector was made of the same material asthat of the positive collector. A gas-liquid separation film was made ofa PTFE film having a pore.

EXAMPLE 2

A catalyst layer of a positive electrode was produced as follows. First,50 parts by weight of “Ketchen Black EC” (Trade Name) produced by LionAkzo Co., Ltd., 7 parts by weight of platinum-supporting carbon with anaverage particle diameter of 5 μm supporting 50% by weight of platinumfine particles with an average particle diameter of 3 nm, 86 parts byweight of a proton conductive material “Nafion” (Trade Name, theconcentration of a solid content is 5% by weight) produced byElectroChem Inc., and 7 parts by weight of water were preparedrespectively. They were mixed and dispersed uniformly with an ultrasonicdisperser, and the obtained slurry was dried under reduced pressure toremove a solvent. Complex particles coagulated by drying were crushedwith a planetary ball mill at a rotation number of 50 rpm for 10minutes. Consequently, complex particles with an average particlediameter of 120 μm were obtained. The obtained complex particles wereweighed and placed so that the amount of platinum became 3.0 mg/cm², andsubjected to pressure forming at a pressure of 16 MPa to form a catalystlayer of a positive electrode.

A catalyst layer of a negative electrode was produced as follows. First,50 parts by weight of “Ketchen Black EC”, 7 parts by weight ofplatinum-supporting carbon with an average particle diameter of 3 μmsupporting 50% by weight of platinum-ruthenium alloy (alloy weight ratio1:1) fine particles with an average particle diameter of 3 nm, 86 partsby weight of the above-mentioned “Nafion”, and 7 parts by weight ofwater were prepared respectively. They were mixed and disperseduniformly with an ultrasonic disperser, and the obtained slurry wasdried under reduced pressure to remove a solvent. Complex particlescoagulated by drying were crushed with a planetary ball mill at arotation number of 50 rpm for 10 minutes. Consequently, complexparticles with an average particle diameter of 110 μm were obtained. Theobtained complex particles were weighed and placed so that the amount ofplatinum-ruthenium became 3.0 mg/cm², and subjected to pressure formingat a pressure of 16 MPa to form a catalyst layer of a negativeelectrode. The electrode area was set to be 10 cm² in both the positiveand negative electrodes.

Next, “Nafion 117” (Trade Name, thickness: 180 μm) that was a solidelectrolyte was sandwiched between the catalyst layer of the positiveelectrode and the catalyst layer of the negative electrode formed asdescribed above, and the resultant laminate was heat-pressed at 120° C.for 3 minutes under the condition of 10 MPa, whereby anelectrode-electrolyte assembly was produced. The electrode area was setto be 10 cm² in both the positive and negative electrodes.

The cross-section of the obtained electrode-electrolyte assembly wasobserved with an electron microscope, revealing that the thickness ofthe catalyst layer of the positive electrode was 70 μm, and thethickness of the catalyst layer of the negative electrode was 75 μm. Thepore distribution of each catalyst layer of the obtainedelectrode-electrolyte assembly was measured with a mercury porosimeter“Pore Sizer 9310” (Trade Name) produced by Micromeritics. Consequently,in any of the catalyst layers, the volume of a pore with a pore diameterof 0.3 μm to 2.0 μm was 15% with respect to the total pore volume.

A liquid fuel cell was produced in the same way as in Example 1, exceptfor using the above-mentioned electrode-electrolyte assembly.

EXAMPLE 3

A catalyst layer of a positive electrode was produced as follows. First,50 parts by weight of “Ketchen Black EC” (Trade Name) produced by LionAkzo Co., Ltd., 7 parts by weight of platinum-supporting carbon with anaverage particle diameter of 5 μm supporting 50% by weight of platinumfine particles with an average particle diameter of 3 nm, 86 parts byweight of a proton conductive material “Nafion” (Trade Name, theconcentration of a solid content is 5% by weight) produced byElectroChem Inc., and 7 parts by weight of water were preparedrespectively. They were mixed and dispersed uniformly with an ultrasonicdisperser, and the obtained slurry was granulated by a spray dry method.Consequently, complex particles with an average particle diameter of 30μm were obtained.

Next, 10 parts by weight of the obtained complex particles were added to89 parts by weight of water and one part by weight of 1-propanol, andthe resultant mixture was stirred with a stirrer at a rotation number of100 rpm for one minute, whereby a slurry with the complex particlesdispersed therein was obtained. The obtained slurry was applied to onesurface of a solid electrolyte “Nafion 117” (Trade Name, thickness: 180μm) produced by Dupont so that the amount of platinum became 3.0 mg/cm²,followed by drying, whereby a catalyst layer of a positive electrode wasformed on one surface of the solid electrolyte.

A catalyst layer of a negative electrode was produced as follows. First,50 parts by weight of the above-mentioned “Ketchen Black EC”, 7 parts byweight of platinum-supporting carbon with an average particle diameterof 3 μm supporting 50% by weight of platinum-ruthenium alloy (alloyweight ratio 1:1) fine particles with an average particle diameter of 3nm, 86 parts by weight of the above-mentioned “Nafion”, and 7 parts byweight of water were prepared respectively. They were mixed anddispersed uniformly with an ultrasonic disperser, and the obtainedslurry was granulated by a spray dry method. Consequently, complexparticles with an average particle diameter of 28 μm were obtained.Next, a catalyst layer of a negative electrode was obtained in the sameway as in the positive electrode, except that the complex particles wereapplied to one surface of the solid electrolyte opposite to the surfacewhere the catalyst layer of the positive electrode has been formed sothat the amount of platinum-ruthenium became 3.0 mg/cm².

Next, the laminate of the catalyst layer of the positive electrode, thesolid electrolyte, and the catalyst layer of the negative electrodeformed as described above was heat-pressed at 120° C. for 3 minutesunder the condition of 10 MPa, whereby an electrode-electrolyte assemblywas produced. The electrode area was set to be 10 cm² in both thepositive and negative electrodes.

The cross-section of the obtained electrode-electrolyte assembly wasobserved with an electron microscope, revealing that the thickness ofthe catalyst layer of the positive electrode was 60 μm, and thethickness of the catalyst layer of the negative electrode was 62 μm. Thepore distribution of each catalyst layer of the obtainedelectrode-electrolyte assembly was measured with a mercury porosimeter“Pore Sizer 9310” (Trade Name) produced by Micromeritics. Consequently,in any of the catalyst layers, the volume of a pore with a pore diameterof 0.3 μm to 2.0 μm was 13% with respect to the total pore volume.

A liquid fuel cell was produced in the same way as in Example 1, exceptfor using the above-mentioned electrode-electrolyte assembly.

EXAMPLE 4

An oxidation catalyst layer was formed on a solid electrolyte asfollows. First, 7% by weight of platinum-supporting silica with anaverage particle diameter of 20 nm, and 93% by weight of a protonconductive material “Nafion” (Trade Name, the concentration of a solidcontent is 5% by weight) produced by ElectroChem Inc. were mixed anddispersed uniformly with an ultrasonic disperser, and the obtainedslurry was applied to one surface of a solid electrolyte “Nafion 117”(Trade Name, thickness: 180 μm) produced by Dupont so that the amount ofplatinum became 1.0 mg/cm², followed by drying, whereby an oxidationcatalyst layer was formed on one surface of a solid electrolyte. Theplatinum-supporting silica is composed of silica with an averageparticles size of 20 nm and platinum fine particles with an averageparticle diameter of 5 nm. The weight ratio between silica and platinumfine particles is 100 parts by weight of platinum fine particles withrespect to 100 parts by weight of silica. Furthermore, the oxidationcatalyst layer contains 66 parts by weight of the above-mentioned“Nafion” with respect to the 100 parts by weight of platinum-supportingsilica.

Furthermore, a catalyst layer of a positive electrode was produced asfollows. First, 50 parts by weight of “Ketchen Black EC” (Trade Name)produced by Lion Akzo Co., Ltd., 7 parts by weight ofplatinum-supporting carbon with an average particle diameter of 5 μmsupporting 50% by weight of platinum fine particles with an averageparticle diameter of 3 nm, 86 parts by weight of a proton conductivematerial “Nafion” (Trade Name, the concentration of a solid content is5% by weight) produced by ElectroChem Inc., and 7 parts by weight ofwater were prepared respectively. They were mixed and disperseduniformly with an ultrasonic disperser, and the obtained slurry wasgranulated by a spray dry method. Consequently, complex particles withan average particle diameter of 30 μm were obtained.

Next, 10 parts by weight of the obtained complex particles were added to89 parts by weight of water and one part by weight of 1-propanol, andthe resultant mixture was stirred with a stirrer at a rotation number of100 rpm for one minute, whereby a slurry with the complex particlesdispersed therein was obtained. The obtained slurry was applied to theoxidation catalyst layer provided on the solid electrolyte so that theamount of platinum became 3.0 mg/cm², followed by drying, whereby acatalyst layer of a positive electrode was formed.

A catalyst layer of a negative electrode was produced as follows. First,50 parts by weight of the above-mentioned “Ketchen Black EC”, 7 parts byweight of platinum-supporting carbon with an average particle diameterof 3 μm supporting 50% by weight of platinum-ruthenium alloy (alloyweight ratio 1:1) fine particles with an average particle diameter of 3nm, 86 parts by weight of the above-mentioned “Nafion”, and 7 parts byweight of water were prepared respectively. They were mixed anddispersed uniformly with an ultrasonic disperser, and the obtainedslurry was granulated by a spray dry method. Consequently, complexparticles with an average particle diameter of 28 μm were obtained.Next, a catalyst layer of a negative electrode was formed in the sameway as in the positive electrode, except that the complex particles wereapplied to one surface of the solid electrolyte opposite to the surfacewhere the catalyst layer of the positive electrode has been formed sothat the amount of platinum-ruthenium became 3.0 mg/cm².

Next, the laminate of the catalyst layer of the positive electrode, theoxidation catalyst layer, the solid electrolyte, and the catalyst layerof the negative electrode formed as described above was heat-pressed at120° C. for 3 minutes under the condition of 10 MPa, whereby anelectrode-electrolyte assembly was produced. The electrode area was setto be 10 cm² in both the positive and negative electrodes.

The cross-section of the obtained electrode-electrolyte assembly wasobserved with an electron microscope, revealing that the thickness ofthe catalyst layer of the positive electrode was 60 μm, the thickness ofthe oxidation catalyst layer was 10 μm, and the thickness of thecatalyst layer of the negative electrode was 62 μm. The poredistribution of each catalyst layer of the obtainedelectrode-electrolyte assembly was measured with a mercury porosimeter“Pore Sizer 9310” (Trade Name) produced by Micromeritics. Consequently,in any of the catalyst layers, the volume of a pore with a pore diameterof 0.3 μm to 2.0 μm was 13% with respect to the total pore volume.

A liquid fuel cell was produced in the same way as in Example 1, exceptfor using the above-mentioned electrode-electrolyte assembly.

COMPARATIVE EXAMPLE 1

A catalyst layer of a positive electrode was produced as follows. First,50 parts by weight of “Ketchen Black EC” (Trade Name) produced by LionAkzo Co., Ltd., 7 parts by weight of platinum-supporting carbon with anaverage particle diameter of 5 μm supporting 50% by weight of platinumfine particles with an average particle diameter of 3 nm, 86 parts byweight of a proton conductive material “Nafion” (Trade Name, theconcentration of a solid content is 5% by weight) produced byElectroChem Inc., and 7 parts by weight of water were preparedrespectively. They were mixed and dispersed uniformly with an ultrasonicdisperser, and the obtained slurry was applied to one surface of a solidelectrolyte “Nafion 117” (Trade Name, thickness: 180 μm) produced byDupont so that the amount of platinum became 3.0 mg/cm², followed bydrying, whereby a catalyst layer of a positive electrode was formed onone surface of the solid electrolyte.

A catalyst layer of a negative electrode was produced as follows. First,50 parts by weight of the above-mentioned “Ketchen Black EC”, 7 parts byweight of platinum-supporting carbon with an average particle diameterof 3 μm supporting 50% by weight of platinum-ruthenium alloy (alloyweight ratio 1:1) fine particles with an average particle diameter of 3nm, 86 parts by weight of the above-mentioned “Nafion”, and 7 parts byweight of water were prepared respectively. They were mixed anddispersed uniformly with an ultrasonic disperser, and the obtainedslurry was applied to one surface of the solid electrolyte opposite tothe surface where the catalyst layer of the positive electrode has beenformed so that the amount of platinum-ruthenium became 3.0 mg/cm²,followed by drying, whereby a catalyst layer of a negative electrode wasformed on one surface of the solid electrolyte.

Next, the laminate of the catalyst layer of the positive electrode, thesolid electrolyte, and the catalyst layer of the negative electrodeformed as described above was heat-pressed at 120° C. for 3 minutesunder the condition of 10 MPa, whereby an electrode-electrolyte assemblywas produced. The electrode area was set to be 10 cm² in both thepositive and negative electrodes.

The cross-section of the obtained electrode-electrolyte assembly wasobserved with an electron microscope, revealing that the thickness ofthe catalyst layer of the positive electrode was 80 μm, and thethickness of the catalyst layer of the negative electrode was 90 μm. Thepore distribution of each catalyst layer of the obtainedelectrode-electrolyte assembly was measured with a mercury porosimeter“Pore Sizer 9310” (Trade Name) produced by Micromeritics. Consequently,in any of the catalyst layers, the volume of a pore with a pore diameterof 0.3 μm to 2.0 μm was 2.5% with respect to the total pore volume.

A liquid fuel cell was produced in the same way as in Example 1, exceptfor using the above-mentioned electrode-electrolyte assembly.

COMPARATIVE EXAMPLE 2

A catalyst layer of a positive electrode was produced as follows. First,50 parts by weight of “Ketchen Black EC” (Trade Name) produced by LionAkzo Co., Ltd., 7 parts by weight of platinum-supporting carbon with anaverage particle diameter of 5 μm supporting 50% by weight of platinumfine particles with an average particle diameter of 3 nm, 86 parts byweight of a proton conductive material “Nafion” (Trade Name, theconcentration of a solid content is 5% by weight) produced byElectroChem Inc., and 7 parts by weight of water were preparedrespectively. They were mixed and dispersed uniformly with an ultrasonicdisperser, and the obtained slurry was dried under reduced pressure toremove a solvent. Complex particles coagulated by drying were crushedwith a planetary ball mill at a rotation number of 300 rpm for 6 hours.Consequently, complex particles with an average particle diameter of 2.5μm were obtained.

Next, 10 parts by weight of the obtained complex particles were added to89 parts by weight of water and one part by weight of 1-propanol, andthe resultant mixture was stirred with a stirrer at a rotation number of100 rpm for one minute, whereby a slurry with the complex particlesdispersed therein was obtained. The obtained slurry was applied to onesurface of a solid electrolyte “Nafion 117” (Trade Name, thickness: 180μm) produced by Dupont so that the amount of platinum became 3.0 mg/cm²,followed by drying, whereby a catalyst layer of a positive electrode wasformed on one surface of the solid electrolyte.

A catalyst layer of a negative electrode was produced as follows. First,50 parts by weight of the above-mentioned “Ketchen Black EC”, 7 parts byweight of platinum-supporting carbon with an average particle diameterof 3 μm supporting 50% by weight of platinum-ruthenium alloy (alloyweight ratio 1:1) fine particles with an average particle diameter of 3nm, 86 parts by weight of the above-mentioned “Nafion”, and 7 parts byweight of water were prepared respectively. They were mixed anddispersed uniformly with an ultrasonic disperser, and the obtainedslurry was dried under reduced pressure to remove a solvent. Complexparticles coagulated by drying were crushed with a planetary ball millat a rotation number of 300 rpm for 6 hours. Consequently, complexparticles with an average particle diameter of 2.5 μm were obtained.Next, a catalyst layer of a negative electrode was formed in the sameway as in the positive electrode, except that the complex particles wereapplied to one surface of the solid electrolyte opposite to the surfacewhere the catalyst layer of the positive electrode has been formed sothat the amount of platinum-ruthenium became 3.0 mg/cm².

Next, the laminate of the catalyst layer of the positive electrode, thesolid electrolyte, and the catalyst layer of the negative electrodeformed as described above was heat-pressed at 120° C. for 3 minutesunder the condition of 10 MPa, whereby an electrode-electrolyte assemblywas produced. The electrode area was set to be 10 cm² in both thepositive and negative electrodes.

The cross-section of the obtained electrode-electrolyte assembly wasobserved with an electron microscope, revealing that the thickness ofthe catalyst layer of the positive electrode was 36 μm, and thethickness of the catalyst layer of the negative electrode was 38 μm. Thepore distribution of each catalyst layer of the obtainedelectrode-electrolyte assembly was measured with a mercury porosimeter“Pore Sizer 9310” (Trade Name) produced by Micromeritics. Consequently,in any of the catalyst layers, the volume of a pore with a pore diameterof 0.3 μm to 2.0 μm was 2.7% with respect to the total pore volume.

A liquid fuel cell was produced in the same way as in Example 1, exceptfor using the above-mentioned electrode-electrolyte assembly.

The outputs obtained by applying a current of 20 mA per unit area of anelectrode to the liquid fuel cells produced as described above at roomtemperature (25° C.) were measured. Table 1 shows the results togetherwith the ratio of the volume of a pore with a pore diameter of 0.3 μm to2.0 μm. TABLE 1 Ratio of pore Output volume (%) (mW/cm²) Example 1 10 55Example 2 15 48 Example 3 13 53 Example 4 13 60 Comparative Example 12.5 30 Comparative Example 2 2.7 27

As is apparent from Table 1, the outputs in Examples 1 to 4 are higherthan those in Comparative Examples 1 and 2. The reason for this isconsidered as follows: the pore configuration in the catalyst layer isoptimized in Examples 1 to 4. Particularly, in Example 4 in which anoxidation catalyst layer was provided between the solid electrolyte andthe catalyst layer of the positive electrode, the influence ofcross-over of methanol was less, whereby a higher output was obtained.

INDUSTRIAL APPLICABILITY

As described above, a liquid fuel cell using an electric powergenerating element for a liquid fuel cell of the present inventionexhibits the performance of a catalyst sufficiently, and enables anincomparably high electric power generation efficiency to be obtained,whereby the liquid fuel cell can be miniaturized and have a highercapacity. Therefore, when the liquid fuel cell is used as a power sourcefor a cordless appliance such as a personal computer and a mobiletelephone, the miniaturization and reduction in weight of the cordlessappliance can be achieved.

1. An electric power generating element for a liquid fuel cell,comprising: a positive electrode for reducing oxygen; a negativeelectrode for oxidizing fuel; and a solid electrolyte placed between thepositive electrode and the negative electrode, wherein the positiveelectrode and the negative electrode respectively include a catalystlayer with a thickness of 20 μm or more, at least one of the respectivecatalyst layers has a pore with a pore diameter in a range of 0.3 μm to2.0 μm, and a pore volume of the pore is 4% or more with respect to atotal pore volume.
 2. The electric power generating element for a liquidfuel cell according to claim 1, wherein the catalyst layer contains, asa catalyst, at least one selected from the group consisting of platinum,a platinum-iron alloy, a platinum-nickel alloy, a platinum-cobalt alloy,a platinum-tin alloy, a platinum-ruthenium alloy, and a platinum-goldalloy.
 3. The electric power generating element for a liquid fuel cellaccording to claim 2, wherein the catalyst is supported on a conductivematerial.
 4. The electric power generating element for a liquid fuelcell according to claim 3, wherein the conductive material is carbonpowder.
 5. The electric power generating element for a liquid fuel cellaccording to claim 1, wherein an oxidation catalyst layer for oxidizingliquid fuel is further placed between the solid electrolyte and thecatalyst layer of the positive electrode.
 6. The electric powergenerating element for a liquid fuel cell according to claim 5, whereinthe oxidation catalyst layer contains an insulating material and aproton conductive material.
 7. The electric power generating element fora liquid fuel cell according to claim 5, wherein the oxidation catalystlayer contains a complex material in which a catalyst oxidizing liquidfuel is supported on an insulating material.
 8. The electric powergenerating element for a liquid fuel cell according to claim 5, whereinthe oxidation catalyst layer has a porous configuration.
 9. The electricpower generating element for a liquid fuel cell according to claim 5,wherein a thickness of the oxidation catalyst layer is in a range of 1μm to 200 μm.
 10. A liquid fuel cell comprising the electric powergenerating element for a liquid fuel cell and liquid fuel, the electricpower generating element for a liquid fuel cell comprising: a positiveelectrode for reducing oxygen: a negative electrode for oxidizing fuel:and a solid electrolyte placed between the positive electrode and thenegative electrode, wherein the positive electrode and the negativeelectrode respectively include a catalyst layer with a thickness of 20μm or more, at least one of the respective catalyst layers has a porewith a pore diameter in a range of 0.3 μm to 2.0 μm, and a pore volumeof the pore is 4% or more with respect to a total pore volume.
 11. Theliquid fuel cell according to claim 10, wherein the liquid fuel is amethanol aqueous solution.
 12. A method for producing an electric powergenerating element for a liquid fuel cell comprising a positiveelectrode for reducing oxygen, a negative electrode for oxidizing fuel,and a solid electrolyte placed between the positive electrode and thenegative electrode, the positive electrode and the negative electroderespectively including a catalyst layer with a thickness of 20 μm ormore, at least one of the respective catalyst layers having a pore witha pore diameter in a range of 0.3 μm to 2.0 μm, and a pore volume of thepore being 4% or more with respect to a total pore volume, the method,as a production process of the catalyst layer, comprising: dispersing amaterial containing a catalyst and a proton conductive material in asolvent; forming complex particles by removing the solvent to coagulatethe material; and crushing the complex particles.
 13. The method forproducing an electric power generating element for a liquid fuel cellaccording to claim 12, wherein the catalyst is at least one selectedfrom the group consisting of platinum, a platinum-iron alloy, aplatinum-nickel alloy, a platinum-cobalt alloy, a platinum-tin alloy, aplatinum-ruthenium alloy, and a platinum-gold alloy
 14. The method forproducing an electric power generating element for a liquid fuel cellaccording to claim 12, wherein the catalyst is supported on a conductivematerial.
 15. The method for producing an electric power generatingelement for a liquid fuel cell according to claim 14, wherein theconductive material is carbon powder.
 16. A method for producing anelectric power generating element for a liquid fuel cell comprising apositive electrode for reducing oxygen, a negative electrode foroxidizing fuel, and a solid electrolyte placed between the positiveelectrode and the negative electrode, the positive electrode and thenegative electrode respectively including a catalyst layer with athickness of 20 μm or more, at least one of the respective catalystlayers having a pore with a pore diameter in a range of 0.3 μm to 2.0μm, and a pore volume of the pore being 4% or more with respect to atotal pore volume, the method, as a production process of the catalystlayer, comprising: forming complex particles by granulating a materialcontaining a catalyst and a proton conductive material.
 17. The methodfor producing an electric power generating element for a liquid fuelcell according to claim 16, wherein the catalyst is at least oneselected from the group consisting of platinum, a platinum-iron alloy, aplatinum-nickel alloy, a platinum-cobalt alloy, a platinum-tin alloy, aplatinum-ruthenium alloy, and a platinum-gold alloy
 18. The method forproducing an electric power generating element for a liquid fuel cellaccording to claim 16, wherein the catalyst is supported on a conductivematerial.
 19. The method for producing an electric power generatingelement for a liquid fuel cell according to claim 18, wherein theconductive material is carbon powder.